Considerable effort has gone into developing means for anchoring roof bolts as part of an effort to prevent roof collapses in mines. Obviously, there are many other applications that require grouting of an anchor element in a hole of support structure.
The common commercial anchor element cartridge in use today comprises reactive components of a resin with the components in separate compartments of an elongated tubular casing which are brought into contact with one another upon injecting a bolt,
The reaction of the reactive components of the resin can cause serious health hazards to those people who have to work in the mines.
Therefore, efforts have been made to produce anchor element cartridges which would provide effective fastening for the anchor element in a hole of a support structure and not cause harmful side effects of toxicity or sensitization of allergy-prone persons. One such successful solution to this problem is disclosed in U.S. Pat. No. 4,096,944, incorporated herein by reference, wherein an anchor element cartridge is described comprising water-containing microcapsules which are pressure sensitive combined with non-pressure sensitive hydraulic cement powder. When an anchor element is injected into the elongated cartridge which is in an elongated bore hole in the roof of a mine, the pressure from the anchor element causes a reaction to take place between the hydraulic cement powder and the water which is released from the pressure sensitive microcapsules. These cartridges do an effective job of anchoring without the harmful effects of the resin cartridges. These hydraulic cement cartridges also, at present, have potential ecomomic advantages over resin cartridges due to less expensive material and/or manufacturing costs.
However, a major problem that has arisen with respect to the hydraulic cement cartridges is the difficulty of insertion of the cartridge into the hole in the mine roof. Also related to this are problems of lack of consistent cartridge quality, which has resulted in some poor bonds of the roof bolt to the mine roof.
These problems appear to be related to the problems of manufacture wherein the cartridge filler ingredients are not mixed uniformly in the final cartridge, the final cartridge has weakness planes, and in general there is a lack of uniform compaction of the ingredients in the final cartridge. The final cartridges then have a "rope-like" quality that makes it very difficult to insert, for example, in a small hole in a mine roof. Workers would like to be able to insert the cartridges into the hole with one hand. Instead they have difficulties with both hands. Also the difficulties of getting the cartridge in the hole can cause work delays due to damage caused to cartridges in getting them into the hole, then having to remove the damaged cartridge, and start over with a new cartridge. The damaged cartridge also results in expensive waste of materials. This can result in lost time during installation, as well as cartridges that are damaged during installation thus requiring replacement, or cartridges that only go part way into the hole.
An additional problem which appears to have contributed to inconsistent bonding of the roof bolt is the fact that during insertion of the metal roof bolt the tubular casing often jams the hole in accordian fashion, or alternatively acts as a cover to the inside of the hole in the mine ceiling therefore preventing contact, and bonding, between the reacted cartridge ingredients and the wall of the hole.
The net result of these problems is that any economic advantages that the hydraulic cement cartridges have over the commonly used resin cartridges are significantly diminished or lost. Furthermore, operator resistance to utilizing such difficult to install cartridges would likely be an insurmountable barrier to their general usage, even if there were some economic and ecological advantages to their usage.